Breaker pole parts or plastic component part units of the type described at the outset include vacuum interrupter chambers which are embedded in insulating material or are encapsulated with said material. The vacuum interrupter chambers (VK) themselves substantially comprise a ceramic material (insulator), which is generally cylindrical and is closed at the ends in most cases by a metallic cover. A folding bellows is arranged on the cover on the movable side(s), which folding bellows permits a movement of one or else both contact pieces over a current feed line within the vacuum interrupter chamber. The current feed line is guided via a drive rod in such a way that the contact pieces can be opened or closed within the vacuum of the VK. As mentioned, a vacuum atmosphere is located within the vacuum interrupter chambers in order that as rapid quenching as possible of the arc produced during switching-on and switching-off can be ensured.
These vacuum interrupter chambers are generally encapsulated by a thermosetting-plastic epoxy resin mixture (at ambient pressure or a few bar), which mixture contributes to increasing the external dielectric strength of a vacuum interrupter chamber and takes on mechanical functions. Furthermore, the vacuum interrupter chamber can be encased by a rubber-elastic material likewise for the purpose of increasing the external dielectric strength.
The ceramic insulator of a vacuum interrupter chamber and the encapsulating epoxy resin have a markedly different coefficient of thermal expansion, however, which results in the fact that, if the vacuum interrupter chambers are cast directly into epoxy resin, this epoxy resin sleeve remains sensitive to cracks given corresponding thermal cycling. In addition, the production process is matched to the casting resin encapsulating material. The production times (cycle time) of each component part, for example produced in the vacuum casting process or pressure gelation process, are correspondingly long until curing of the component part and its removal.
In order to avoid possible initiation of cracks, it is known and provided in the prior art to introduce a so-called damping layer or a compensating layer for the purpose of compensating for these different coefficients of thermal expansion between the vacuum interrupter chamber surface and the epoxy resin sleeve. For this purpose, elastomers such as rubber or hard rubber materials are usually used which are in the form of collars or have previously been cast on and applied over the vacuum interrupter chambers before the latter are introduced into a corresponding casting mold and are encapsulated with epoxy resin (usually with a filler). Said compensating layer is in this case also cast into the composite produced.
This manufacturing process which is advantageous per se prevents the possibility of cracking of the epoxy resin casing occurring after casting or given thermal cycling.
The production of an epoxy resin casing as such remains extremely complex, however.